Efficient photocatalytic CO₂ N-formylation of amines over Pd/Bi-ZnO_x without extra reductant

Photocatalytic N-formylation of amines with CO₂ is a promising strategy to convert CO₂ into value-added chemicals sustainably. In this work, Pd-Bi bimetallic modified ZnO enriched in oxygen vacancies is constructed for photocatalytic CO₂ formylation of benzylamine at room temperature without any reductants. The Pd and Bi sites reduce the band gap energy of ZnO, promote the separation of the photogenerated charge carriers and enhance the adsorption capacity of CO₂. The yield of N-benzylformamide reaches 31.7 mmol g⁻¹ with a selectivity of 85.3 % after 3-hour radiation in N,N-dimethylformamide (DMF) solvent. The aldehyde group involved in the formylation of benzylamine is derived from the decomposition of DMF, which is regenerated with the aldehyde group coming from the reduction of CO₂. The decomposition-regeneration cycle of DMF solvent enlarges the reaction region, which is beneficial to the activity and selectivity of the formylation process. The synergistic photocatalytic system shows a good universality. This study provides a new approach to high-efficiency CO₂ utilization and formamide production.